With the HIV seroprevalence rate among pregnant women exceeding 25% in many low resource settings in sub-Saharan Africa, the challenge of reducing postnatal HIV transmission through breastfeeding without compromising the health and nutrition of infants remains formidable. For reasons of feasibility and safety, many HIV-infected women in these settings continue to initiate breastfeeding. Several programs now advocate early (<6 months) cessation of breastfeeding. An under-researched topic is how HIV-infected women should safely transition from breastfeeding to no breastfeeding i.e. the weaning process. Ordinarily, women gradually introduce complementary foods while continuing to breastfeed into the child's second year and breast milk replacements are not required. In the case of HIV-infected women, several programs, including our own, have encouraged rapid weaning for HIV-infected women who intend to stop breastfeeding early. The motivation for this unusual practice is to avoid or shorten any period of mixed breastfeeding. However, our preliminary data indicate that rapid weaning is associated with adverse maternal and child health outcomes and may facilitate postnatal HIV transmission. We hypothesize that the physiological changes associated with rapid weaning (increased mammary permeability and inflammation) increase HIV levels in maternal milk and blood thereby significantly increasing the risk of HIV transmission. The objective of this application is to test these hypotheses using well-characterized samples from a recently-completed clinical trial. These studies will provide critical information on how the weaning transition can be made safer for HIV-infected women and their children. The specific aims are to: (1) compare the virologic dynamics of breast milk HIV-1 cell-free RNA and cell-associated proviral DNA in rapid weaning compared to gradual weaning;(2) characterize changes in breast milk markers of mammary inflammation and epithelial permeability which may contribute to the increased HIV transmission associated with rapid weaning;(3) investigate the behavioral and clinical factors that may ameliorate these breast milk changes;(4) examine the effects of rapid weaning on acute and longer- term maternal morbidity as well as changes in plasma viral load and CD4 counts;and (5) investigate parameters of infant feeding and weaning behaviors associated with child morbidity and growth among HIV- infected and HIV-exposed uninfected infants. Regardless of the duration of breastfeeding, and regardless of whether or not antiretroviral drugs are taken, HIV-infected women who initiate some breastfeeding will inevitably have to wean at some time. Thus it is important that the effects of different strategies be empirically evaluated to develop evidence-based nutrition counseling messages for HIV-infected women about safer practices around the time of weaning.Project Narrative Several programs recommend that HIV-infected women rapidly wean their infants at 6 months or earlier but our preliminary data suggest that this practice may have adverse consequences. We propose to test the hypothesis that physiological changes associated with rapid weaning (increased mammary permeability and inflammation) increase viral levels in breast milk and blood thereby increasing risks of HIV transmission. Our goal is to develop evidence-based nutrition counseling messages about safer practices for HIV-infected women and their infants around the time of weaning.